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That's an extremely weak argument. Java's Optional is broken and should never be used.
by premium-concern 10y ago
That's an extremely weak argument. Java's Optional is broken and should never be used.
- cle 10y agoIf that is true, then it's another example supporting my point.
- premium-concern 10y agoNo. Java messing things up as usual, doesn't have any broader impact on the usefulness of the concept. Error handling with null is wrong and broken, regardless of whether the null is "typed" or not. null might have some very limited other uses, but they will never compete with those structures designed for error handling, because they do something fundamentally different.
- cle 10y agoMy argument is practical, not theoretical. Platitudes and ideals are disposable when you have to actually build something.
- premium-concern 10y agoYawn. Java is the platform with NPEs and null checks everywhere. If that's your definition of practical, sure, go ahead.
- dllthomas 10y agoCould you expand on this?
- premium-concern 10y agoOptional#map is implemented incorrectly. someOptional.map(a).map(b) NOT EQUAL TO someOptional.map(a.andThen(b)
- dllthomas 10y agoAh, that's unfortunate. Because of the order in which side effects occur, or is there something else as well? (I haven't Javaed in anger since before Optional).
- premium-concern 10y agoConsider two functions (excuse my Scala): scala> val str: Function[String, String] = s => if (s.length > 3) s else null str: java.util.function.Function[String,String] = $$Lambda$1369/859456754@2c668c2a scala> val num: Function[String, Integer] = s => if (s == null) -1 else s.length num: java.util.function.Function[String,Integer] = $$Lambda$1376/1887041776@121cf6f4 With Optional, you receive different results depending on whether you call map twice, or combine the functions first: scala> Optional.of("Foo").map[String](str).map[Integer](num) res12: java.util.Optional[Integer] = Optional.empty scala> Optional.of("Foo").map[Integer](str.andThen(num)) res15: java.util.Optional[Integer] = Optional[-1] This is incorrect. (They decided to disallow null as Optional's value for whatever insane reason.) It also leads to all sort of weird usability issues: The old "`someMap.get(...)` returned null ... now does that mean the entry doesn't exist, or the entry exists and it is null?" In fact they are currently working on special hacks to Java 10's Generics, because they realized that important collection classes don't work well with specialization, and even their new Optional can't save them. (Not directly related, but a good example how design mistakes combine and cause even more pain down the road.)
- dllthomas 10y agoInteresting, thanks!